Linear transformer drivers (LTDs) are a relatively new technology being developed because of their potential to provide high performance and greater versatility of applications at a significantly reduced cost. LTDs can potentially achieve compactness and low cost by going directly from DC-charged capacitors to a 100-ns pulse propagating on a vacuum or water transmission line, without any of the pulse-compression sections normally associated with large pulsed-power drivers. See E. A. Weinbrecht et al., Proc. 15th IEEE Pulsed Power Conf., 170 (2005); D. Johnson et al., Proc. 15th IEEE Pulsed Power Conf., 314 (2005); I. D. Smith et al., IEEE Trans. Plasma Sci. 28, 1653 (2000); J. J. Ramirez et al., Proc. 7th IEEE Pulsed Power Conf., 26 (1989); K. R. Lechien et al., Phys. Rev. ST Accel. Beams 11, 060401 (2009); J. R. Woodworth et al., IEEE Trans. Plasma Sci. 32, 1778 (2004); and P. Sincerny et al., Proc. 11th IEEE Pulsed Power Conf., 698 (1997). However, in order to induce a voltage pulse in a magnetically insulated vacuum transmission line with a ˜70 ns or less rise time, the inductance of the capacitors, switch, and the transmission line leading to the vacuum section of the LTD must be minimized.
Therefore, the switches required to power LTDs must be reliable and perform within precise parameters that include low inductance, low jitter, and high longevity. In particular, LTDs require gas switches that can be DC charged to ˜200 kV, triggered with ˜5-10 ns one sigma jitter, be low inductance, have very low prefire and no-fire rates, and have lifetimes of at least several thousand shots. See J. R. Woodworth et al., Phys. Rev. ST Accel. Beams 12, 060401 (2009), which is incorporated herein by reference. FIG. 1 shows a cross-sectional side view illustration of a prior gas switch 10 designed by Kinetech, LLC and described in Woodworth et al. This switch 10 is axially symmetric about a centerline. The distance between electrodes 11 and 12 can be varied by screwing the insertable end pieces 13 and 14 in and out along the threads in the main outer “barrel” housing 15. The switch with the threads screwed in as far as possible provides the lowest possible inductance configuration. In this configuration, the switch has a diameter of 7.5 cm and is 12 cm long. The end caps 16 and 17 of the switch are clamped in split rings that can bolt directly to the ends of the LTD capacitors. This switch has two hemispherical electrodes 11 and 12 with a 0.95-cm spacing therebetween. Four trigger pins 18 are used instead of one to minimize erosion of the trigger pins that can otherwise limit the lifetime of the switch. The four 0.3-cm diameter trigger pins 18 extend inwardly from the midplane of the housing 15 towards the center of the switch. The spark gap between each trigger pin 18 and the main electrodes 11 and 12 is 0.5 cm. The electrodes 11 and 12 are a copper-tungsten alloy, the trigger pins 18 are pure tungsten, and the end caps 16 and 17 are an aluminum alloy. The gas inlet and outlet ports are also on the midplane of the switch. The outer insulators 13 and 14 and housing 15 are a glass-fiber loaded ULTEM™ plastic and the inner liner 19 is Kel-FTM plastic. The entire switch 10 can be submerged in an insulating fluid during operation.
Since the discharge normally occurs from one electrode to a trigger pin and then from the trigger pin to the other electrode, this switch effectively has two 0.5-cm spark gaps. FIG. 2A shows an electrostatic field plot of the prior switch with 200 kV between the electrodes. For this two-dimensional simulation, the trigger pins were approximated as an annular sheet on the switch midplane. The maximum electric field at the surface of the electrodes was 270 kV/cm. FIG. 2B shows an electrostatic field plot of this switch with the trigger pin at +100 kV as the trigger pulse arrives at the switch. The peak electric field in the switch when the trigger pulse arrives was slightly over 500 kV/cm. This prior switch was very robustly designed, relatively simple, and triggered with less than 5 ns jitter. However, it operated at relatively high pressure (e.g., 242 psia) which can pose problems in some applications. Further, the switch's inductance was surprisingly high (e.g., 100 nH) for a switch this small.
Therefore, a need remains for a high-voltage, low-inductance gas switch that can be used with LTDs and other pulsed-power systems.